Memory implemented error detection and correction code using memory modules

ABSTRACT

A method and apparatus for performing digital signal error detection and correction through the use of a string of received incoming system address bits. The incoming address bits are divided into groups according to whether they contain a high value of &#34;1&#34; or a low value of &#34;0&#34;. At least one address parity bit is then generated from each group and used in checking the integrity of data received. Errors are corrected and detected through assignment of data bits to different modules in a memory of a computer system having symbols which are b bits in length.

BACKGROUND OF THE INVENTION

This application is related in subject matter to two other applications, Ser. Nos. 08/570,446 patented and 08/570,447 both filed on the same day as this application.

The present invention is generally directed to error correction, decoding and encoding systems found in digital devices. The present invention incorporates by reference the invention disclosed in U.S. Ser. No. 08/538,691 filed Oct. 3, 1995 entitled "error detection and correction code for four-bit-per-chip memory system", directed to multibit-per chip computer memory systems in which error correction and detection apparatus are provided to acheive correction of all single symbol errors and the detection of all single symbol errors occurring with a single bit error in a second symbol. More particularly, the present invention is directed to a memory assignment scheme, which assigns error correction code words to selected array modules, and incorporates parity address bits in this assignment scheme in order to provide an error correction and detection method and apparatus capable of detecting a variety of errors, including the detection of data fetched from an erroneous address.

In a computer system having b bits of memory available per chip, the failure of each chip can cause one to b erroneous bits in the output data depending upon the failure mode and the data originally stored. A b bit symbol error pattern is used to indicate one of all of the possible 2^(b) -1 error patterns in the b bits for each computer chip. Normal error correction and detection systems employed in such situations would involve the use of a single error correction (SEC) and double error detection (DED) code. The SEC-DED code, however, is neither effective in correcting symbol errors generated from single chip failures, nor is effective in detecting symbol errors generated from double chip failures. On the other hand, a single symbol error correction and double symbol error detection code, a so-called SSC-DSD code, would provide an effective error correction and detection method to acheive high reliability in a b bit per chip memory. However, SSC-DSD codes require more check bits and more memory chips than are actually necessary for the problem. In particular, for a 64-bit data bus, the required SSC-DSD code would require four redundant memory chips for every 16 data chips to implement a (78,66) SSC-DSD code. Such codes would be 78 bits in length with 64 information bits and 14 check bits. Thus a memory system implementing this code would require 20 chips based upon the above memory organization.

Recognizing the stringent requirements of the SSC-DSD memory system, the present inventors devised a new coding scheme as described in detail in U.S. Ser. No. 08/538,691, in which the number of redundant chips are decreased from 4 to 3 chips for a (76,64) code for each set of 16 chips. This code is then used to correct all single symbol errors and detect all single symbol errors plus a single bit error in a second symbol. In certain instances, however, although the data in storage is error free, an error condition can occur if data is fetched from the wrong address in memory. However, the invention introduced in U.S. Ser. No. 08/538,691 never addressed the issue of detection of data fetched from an erroneous address.

The present invention utilizes the coding scheme suggested in U.S. Ser. No. 08/538,691, but improves upon the code by generating address parity bits from system address bits and later including these in the generation of ECC word. Accordingly, a more efficient and more reliable improved computer memory system is provided through the use of the present invention. All of these are desirable results.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, digital signal encoding and decoding is accomplished by an apparatus and method through assignment of data bits to different modules in a memory of a computer system having symbols which are b bits in length. First a multiplicity, k, of multisegment syndrome vectors in which each segment in each of said k syndrome vector is b bits long is generated.

Information is then retrieved from memory pertaining to assignment of different data blocks to a plurality of modules in the computer system. A multiplicity of module error indicators are then generated from the syndrome vectors. Each module error indicator is associated with at least one of the plurality of modules. In case of an error, the associated module error indicator is set to a value of one. After error is detected, the same is reported and efforts for correcting the error is taken when the error is determined to be of a kind that is correctable, such as a CE (Correctable Error.) When the error detected is a UE or an uncorrectable error, no further correction efforts are undertaken, but the is reported as such to the user.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is an overall block diagram illustrating a memory system in which a memory word is stored on k separate chips each providing b bits to a computer memory system register;

FIG. 2 is a functional block diagram illustrating the 15 possible error patterns for the case in which there are four bits per chip;

FIGS. 3A and 3B are functional block diagrams illustrating the limits of error detectability for the circuits of the present invention;

FIG. 4 is a general ECC (Error Correction Code) flow diagram, illustrating various staging registers and line buffers involved in the store and fetch operations for the present invention;

FIG. 5 is an illustration of the processing of bits during a data store operation;

FIG. 6 is a further illustration of the operation of a data store command according to the concepts presented by the present invention;

FIG. 7 is an illustration of the processing of bits during a data fetch operation;

FIG. 8 is a further illustration of the operation of a data fetch command according to the concepts presented by the present invention;

FIG. 9 illustrates the arrangement of data in memory modules on the SIMM array(s).

DETAILED DESCRIPTION OF THE INVENTION

The invention described below is particularly shown with respect to a particular example, namely the construction of a (76,64) code for a four-bit per chip computer memory system. However, the ideas presented herein are extensible to the general b bit per chip situation. In particular, it is noted that the number of rows of b by b submatrices in the parity check matrix is determined by the error correction capabilities that are desired. In the particular instance of the codes constructed in accordance with the present invention, three rows of by b submatrices are sufficient to provide the desired correction and detection capabilities. Likewise in general, codes constructed in accordance with the present invention will have k symbols. Each symbol will be represented by b bits. Since three of the symbols are employed for redundancy, there are thus k-3 information symbols and 3 symbols which comprise check bits.

With respect to the present invention for a (76,64) code, the parity check matrix for this code including an embodiment utilizing two address parity bits is given below:

                                      TABLE I                                      __________________________________________________________________________                                                         SYMBOL                                                                              ADDRESS                                                                   ID   PARITY                DATA                                       ECC      (CHIP)                                                                              BITS                  1  2 3  4 5  6 7  8 9  10                                                                               11 12 13 14 15 16 17 18 19 ID   20                    __________________________________________________________________________     1000 1000                                                                           1000 1000                                                                           1000 1000                                                                           1000 1000                                                                           1001 1101                                                                           1111                                                                              0011                                                                              1100                                                                              1100                                                                              1110                                                                              0110                                                                              1000                                                                              0000                                                                              0000                                                                              --   01                    0100 0100                                                                           0100 0100                                                                           0100 0100                                                                           0100 0100                                                                           0111 1011                                                                           1010                                                                              0010                                                                              1000                                                                              1000                                                                              1001                                                                              1101                                                                              0100                                                                              0000                                                                              0000                                                                              --   11                    0010 0010                                                                           0010 0010                                                                           0010 0010                                                                           0010 0010                                                                           0111 0110                                                                           1100                                                                              1111                                                                              0011                                                                              0011                                                                              1001                                                                              1011                                                                              0010                                                                              0000                                                                              0000                                                                              --   10                    0001 0001                                                                           0001 0001                                                                           0001 0001                                                                           0001 0001                                                                           1110 1101                                                                           1000                                                                              1010                                                                              0010                                                                              0010                                                                              0111                                                                              0110                                                                              0001                                                                              0000                                                                              0000                                                                              --   11                    0110 1000                                                                           0010 1011                                                                           1010 1101                                                                           0101 1110                                                                           1000 0001                                                                           1000                                                                              0111                                                                              1000                                                                              1110                                                                              1000                                                                              0100                                                                              0000                                                                              1000                                                                              0000                                                                              --   10                    1101 0100                                                                           0001 0110                                                                           0101 1011                                                                           1111 1001                                                                           0100 0011                                                                           0100                                                                              1110                                                                              0100                                                                              1001                                                                              0100                                                                              1100                                                                              0000                                                                              0100                                                                              0000                                                                              --   01                    1011 0010                                                                           1010 1101                                                                           1000 0110                                                                           0100 1001                                                                           0010 0101                                                                           0010                                                                              1110                                                                              0010                                                                              1001                                                                              0010                                                                              0001                                                                              0000                                                                              0010                                                                              0000                                                                              --   00                    0110 0001                                                                           0101 1011                                                                           0100 1101                                                                           1100 0111                                                                           0001 1111                                                                           0001                                                                              1001                                                                              0001                                                                              0111                                                                              0001                                                                              0011                                                                              0000                                                                              0001                                                                              0000                                                                              --   00                    1000 1110                                                                           0111 1010                                                                           1001 0010                                                                           0110 0001                                                                           0101 1000                                                                           1011                                                                              1000                                                                              0110                                                                              1000                                                                              0100                                                                              1000                                                                              0000                                                                              0000                                                                              1000                                                                              --   00                    0100 1001                                                                           1110 0101                                                                           0111 0001                                                                           1101 0011                                                                           1111 0100                                                                           0110                                                                              0100                                                                              1101                                                                              0100                                                                              1100                                                                              0100                                                                              0000                                                                              0000                                                                              0100                                                                              --   00                    0010 1001                                                                           1110 1000                                                                           0111 1010                                                                           1011 0101                                                                           0100 0010                                                                           1101                                                                              0010                                                                              1011                                                                              0010                                                                              0001                                                                              0010                                                                              0000                                                                              0000                                                                              0010                                                                              --   01                    0001 0111                                                                           1001 0100                                                                           1110 0101                                                                           0110 1111                                                                           1100 0001                                                                           1011                                                                              0001                                                                              0110                                                                              0001                                                                              0011                                                                              0001                                                                              0000                                                                              0000                                                                              0001                                                                              --   10                    __________________________________________________________________________

DATA STORE OPERATION

During a store operation, in accordance with the embodiment represented by the parity check matrix shown in Table I, each of the 12 ECC check bits is generated. The 12 ECC check bits are generated in two stages. During the first stage, a partial ECC check bit is generated by exclusive OR circuits which take a subset of 64 data bits as indicated by the 1's in each row of the parity check matrix in Table I. For example, the first partial check bit is generated by exclusive-ORing data found at positions: 1, 5, 9, 13, 17, 21, 25, 29, 33, 36, 37, 38, 40, 41, 42, 43, 44, 47, 48, 49, 50, 53, 54, 57, 58, 59, 62 and 63.

These address parity bits are generated from selective combination of data from system address bits as discussed later in detail. During the second stage the partial check bits are combined with the address parity bits and data bits to generate the final 12 ECC check bits.

The set of 64 data bits together with the 12 check bits form an ECC word. Therefore, it seems that in the embodiment presented in Table I, when the two address parity bits are included, the ECC word is really a (78,66) code word. However, since the parity address bits have been used in the generation of the final 12 ECC check bits, it is unnecessary for them to be stored as part of the ECC word. Therefore, the code is still a (76,64) code since only 76 bits per code word are stored into the memory array or a SIMM (Single-Inline-Memory-Module) as shown in FIG. 9. The address parity bits are regenerated during the fetch operation from the incoming system address bits.

The ECC word is divided into 19 groups of 4 bit symbols. In storing data, the ECC word is stored in 19 different chips. That is each symbol is stored on a different chip. This situation is illustrated in FIG. 1 wherein memory system 10 is shown to be organized using m chips with b bits being delivered from each chip at a time. Thus, the ECC word in register 25 is mb bits long. For the example illustrated herein, m=19 and b=4.

When an array chip, say chip i, fails the data stored in that chip may or may not be in error depending on the data stored. If the data is in error, the number of errors may be one or more than one. FIG. 2 illustrates all of the possible error patterns 2^(b) -1=15 for a failed chip i. FIGS. 3A and 3B illustrate the limits of error detectability in the present invention. FIG. 3A particularly shows the situation in which chip i produces from one to four errors while only a single error occurs in chip j. Reference numeral 20 in FIGS. 1 through 3 refer to the individual memory chips. FIG. 3B shows the situation in which chip i produces from one to four errors while only a single error occurs in address parity bits.

At the outset of a store operation data bits are stored in a plurality of storage buffers. In the example illustrated in Table II, given below, the 64 data bits are first stored in two storage buffers named STBUF₋₋ H₋₋ D(0 . . . 31) and STBUF₋₋ L₋₋ D(0 . . . 31), respectively. There are 32 bits of data in each storage buffer and these bits are renamed as SEC₋₋ O₋₋ H(0 . . . 31) and SEC₋₋ O₋₋ L(0 . . . 31) when wired into the memory modules, namely the modules of a SIMM.

                                      TABLE II                                     __________________________________________________________________________     STBUF.sub.-- H.sub.-- D(0..31)                                                                11                                                                               1111     1111                                                                              2222     2222                                                                              2233                                  0123 4567     8901                                                                              2345     6789                                                                              0123     4567                                                                              8901                                  __________________________________________________________________________     1000 1000     1000                                                                              1000     1000                                                                              1000     1000                                                                              1000                                  0100 0100     0100                                                                              0100     0100                                                                              0100     0100                                                                              0100                                  0010 0010     0010                                                                              0010     0010                                                                              0010     0010                                                                              0010                                  0001 0001     0001                                                                              0001     0001                                                                              0001     0001                                                                              0001                                  0110 1000     0010                                                                              1011     1010                                                                              1101     0101                                                                              1110                                  1101 0100     0001                                                                              0110     0101                                                                              1011     1111                                                                              1001                                  1011 0010     1010                                                                              1101     1000                                                                              0110     0100                                                                              1001                                  0110 0001     0101                                                                              1011     0100                                                                              1101     1100                                                                              0111                                  1000 1110     0111                                                                              1010     1001                                                                              0010     0110                                                                              0001                                  0100 1001     1110                                                                              0101     0111                                                                              0001     1101                                                                              0011                                  0010 1001     1110                                                                              1000     0111                                                                              1010     1011                                                                              0101                                  0001 0111     1001                                                                              0100     1110                                                                              0101     0110                                                                              1111                                  __________________________________________________________________________     STBUF.sub.-- L.sub.-- D(0..31)                                                                         SEC.sub.-- O.sub.-- C(0..11)                                  11                                                                               1111                                                                              1111                                                                              2222                                                                              2222                                                                              2233      11 STORE.sub.-- ADDRP.sub.-- D(0..1)            __________________________________________________________________________     0123                                                                              4567                                                                              8901                                                                              2345                                                                              6789                                                                              0123                                                                              4567                                                                              8901                                                                              0123                                                                              4567                                                                               8901                                                                              01                                           1001                                                                              1101                                                                              1111                                                                              0011                                                                              1100                                                                              1100                                                                              1110                                                                              0110                                                                              1000                                                                              0000                                                                               0000                                                                              01                                           0111                                                                              1011                                                                              1010                                                                              0010                                                                              1000                                                                              1000                                                                              1001                                                                              1101                                                                              0100                                                                              0000                                                                               0000                                                                              11                                           0111                                                                              0110                                                                              1100                                                                              1111                                                                              0011                                                                              0011                                                                              1001                                                                              1011                                                                              0010                                                                              0000                                                                               0000                                                                              10                                           1110                                                                              1101                                                                              1000                                                                              1010                                                                              0010                                                                              0010                                                                              0111                                                                              0110                                                                              0001                                                                              0000                                                                               0000                                                                              11                                           1000                                                                              0001                                                                              1000                                                                              0111                                                                              1000                                                                              1110                                                                              1000                                                                              0100                                                                              0000                                                                              1000                                                                               0000                                                                              10                                           0100                                                                              0011                                                                              0100                                                                              1110                                                                              0100                                                                              1001                                                                              0100                                                                              1100                                                                              0000                                                                              0100                                                                               0000                                                                              01                                           0010                                                                              0101                                                                              0010                                                                              1110                                                                              0010                                                                              1001                                                                              0010                                                                              0001                                                                              0000                                                                              0010                                                                               0000                                                                              00                                           0001                                                                              1111                                                                              0001                                                                              1001                                                                              0001                                                                              0111                                                                              0001                                                                              0011                                                                              0000                                                                              0001                                                                               0000                                                                              00                                           0101                                                                              1000                                                                              1011                                                                              1000                                                                              0110                                                                              1000                                                                              0100                                                                              1000                                                                              0000                                                                              0000                                                                               1000                                                                              00                                           1111                                                                              0100                                                                              0110                                                                              0100                                                                              1101                                                                              0100                                                                              1100                                                                              0100                                                                              0000                                                                              0000                                                                               0100                                                                              00                                           0100                                                                              0010                                                                              1101                                                                              0010                                                                              1011                                                                              0010                                                                              0001                                                                              0010                                                                              0000                                                                              0000                                                                               0010                                                                              01                                           1100                                                                              0001                                                                              1011                                                                              0001                                                                              0110                                                                              0001                                                                              0011                                                                              0001                                                                              0000                                                                              0000                                                                               0001                                                                              10                                           __________________________________________________________________________

The address parity bits are located in address buffers indicated as STORE₋₋ ADDRP₋₋ D(0 . . . 1) in Table II above. The address parity bits are generated from selective combination of data from system address bits as shown in the example provided below in Table III.

                                      TABLE III                                    __________________________________________________________________________      ##STR1##                                                                       ##STR2##                                                                       ##STR3##                                                                       ##STR4##                                                                       ##STR5##                                                                       ##STR6##                                                                       ##STR7##                                                                       ##STR8##                                                                       ##STR9##                                                                       ##STR10##                                                                      ##STR11##                                                                     __________________________________________________________________________      CD means memory card selection bit                                             C0-C11 means Column Address 0-11                                               R0-R11 means Row Address 0-11                                                  EO means even/odd lines (on STC interleaving)                                  RE means RAS A/B decode                                                  

STORE₋₋ ADDRP₋₋ D(0) is generated from the parity of system address bits 1, 2, 5-14, 26, 27 and 30. Similarily, STORE₋₋ ADDRP₋₋ D(1) is the parity of system address bits 0, 3, 4, 5-25, and 31. As illustrated in table III, the mapping of system address bits to memory module depends on the size of the modules.

The final ECC check bits are then generated by combining the contents of the STORE₋₋ ADDRP with the data stored in the storage buffers STBUF and the data obtained from the partial check bits generated from the Exclusive-Or circuitry. In short, during the first stage, the partial check bits SY0(0 . . . 11) are generated from the high word data word STBUF₋₋ H₋₋ D(0 . . . 31) and SY1(0 . . . 11) are generated from the low data word STBUF₋₋ L₋₋ D(0 . . . 31). Then SY0 and SY1 and address parity bits are combined to produce the final check bits. The final 12 ECC check bits are stored in SEC₋₋ O₋₋ C(0 . . . 11) buffer. The following equation illustrates in detail the generation of the 12 ECC check bits and their final storage in the SEC₋₋ O₋₋ C(0 . . . 11) buffer.

The notation OPA(X||Y||Z) is used to describe a logic function that implements the odd parity of bits X,Y and Z. The generation of check bits is divided in two stages as mentioned earlier. ##STR12##

FIG. 4 is an illustration of the general ECC flow diagram. Logic steps 1 through 4, 100 through 400, are the various staging registers and line buffers used in the data store and data fetch operations. Logic steps 1 and 2, 100 and 200, involve different operations that finally allow the generation of ECC store operation 220 into the computer memory DRAM array 500. This information is later fetched from the DRAM array 500 to regenerate and decode the bits during the fetch operation, 300 through 400.

During the store operation, the ECC check bits 57 are generated from the 64 data bits 50 and the system address bits 52 as shown FIG. 5. The entire ECC word 58 is then stored into a memory array 500 to be used later during a fetch operation. FIG. 6 shows the storage of data in storage arrays 61, 62 and 63 before the generation of check bits 66,67 and 68.

Table I above is an embodiment of the present invention utilizing two address parity bits. Other embodiments are conceivable, however, in accordance to the concepts of the present invention where the number of address parity bits, can either be reduced to one or increased to more than two. Table IV given below provides another embodiment of the present invention where eight address parity bits are generated and used.

                                      TABLE IV                                     __________________________________________________________________________                                                         SYMBOL                                                                              ADDRESS                                                                   ID   PARITY                DATA                                       ECC      (CHIP)                                                                              BITS                  1  2 3  4 5  6 7  8 9  10                                                                               11 12 13 14 15 16 17 18 19 ID   20 21                 __________________________________________________________________________     1000 1000                                                                           1000 1000                                                                           1000 1000                                                                           1000 1000                                                                           1001 1101                                                                           1111                                                                              0011                                                                              1100                                                                              1100                                                                              1110                                                                              0110                                                                              1000                                                                              0000                                                                              0000                                                                              --   0111                                                                              1101               0100 0100                                                                           0100 0100                                                                           0100 0100                                                                           0100 0100                                                                           0111 1011                                                                           1010                                                                              0010                                                                              1000                                                                              1000                                                                              1001                                                                              1101                                                                              0100                                                                              0000                                                                              0000                                                                              --   1111                                                                              0010               0010 0010                                                                           0010 0010                                                                           0010 0010                                                                           0010 0010                                                                           0111 0110                                                                           1100                                                                              1111                                                                              0011                                                                              0011                                                                              1001                                                                              1011                                                                              0010                                                                              0000                                                                              0000                                                                              --   1011                                                                              0111               0001 0001                                                                           0001 0001                                                                           0001 0001                                                                           0001 0001                                                                           1110 1101                                                                           1000                                                                              1010                                                                              0010                                                                              0010                                                                              0111                                                                              0110                                                                              0001                                                                              0000                                                                              0000                                                                              --   1100                                                                              1101               0110 1000                                                                           0010 1011                                                                           1010 1101                                                                           0101 1110                                                                           1000 0001                                                                           1000                                                                              0111                                                                              1000                                                                              1110                                                                              1000                                                                              0100                                                                              0000                                                                              1000                                                                              0000                                                                              --   1000                                                                              0011               1101 0100                                                                           0001 0110                                                                           0101 1011                                                                           1111 1001                                                                           0100 0011                                                                           0100                                                                              1110                                                                              0100                                                                              1001                                                                              0100                                                                              1100                                                                              0000                                                                              0100                                                                              0000                                                                              --   0110                                                                              0111               1011 0010                                                                           1010 1101                                                                           1000 0110                                                                           0100 1001                                                                           0010 0101                                                                           0010                                                                              1110                                                                              0010                                                                              1001                                                                              0010                                                                              0001                                                                              0000                                                                              0010                                                                              0000                                                                              --   0001                                                                              0010               0110 0001                                                                           0101 1011                                                                           0100 1101                                                                           1100 0111                                                                           0001 1111                                                                           0001                                                                              1001                                                                              0001                                                                              0111                                                                              0001                                                                              0011                                                                              0000                                                                              0001                                                                              0000                                                                              --   0000                                                                              1110               1000 1110                                                                           0111 1010                                                                           1001 0010                                                                           0110 0001                                                                           0101 1000                                                                           1011                                                                              1000                                                                              0110                                                                              1000                                                                              0100                                                                              1000                                                                              0000                                                                              0000                                                                              1000                                                                              --   0000                                                                              1100               0100 1001                                                                           1110 0101                                                                           0111 0001                                                                           1101 0011                                                                           1111 0100                                                                           0110                                                                              0100                                                                              1101                                                                              0100                                                                              1100                                                                              0100                                                                              0000                                                                              0000                                                                              0100                                                                              --   0001                                                                              1010               0010 1001                                                                           1110 1000                                                                           0111 1010                                                                           1011 0101                                                                           0100 0010                                                                           1101                                                                              0010                                                                              1011                                                                              0010                                                                              0001                                                                              0010                                                                              0000                                                                              0000                                                                              0010                                                                              --   0110                                                                              1000               0001 0111                                                                           1001 0100                                                                           1110 0101                                                                           0110 1111                                                                           1100 0001                                                                           1011                                                                              0001                                                                              0110                                                                              0001                                                                              0011                                                                              0001                                                                              0000                                                                              0000                                                                              0001                                                                              --   1011                                                                              1001               __________________________________________________________________________

DATA FETCH OPERATION

During a Fetch operation, the reverse of the store process implemented during the store operation is used as shown in FIGS. 7 and 8. Data 70, 72 and 55, including the ECC word, is first fetched from memory 500, as shown in FIG. 7. FIG. 9 illustrates the circuits used during an ECC fetch operation. Data fetched from the DRAM array chips are named MDRMUX₋₋ H(0 . . . 31) 92 for modules 1 to 8, MDRMUX₋₋ L(0 . . . 31) 94 for modules 9 to 16 and MDRMUX₋₋ C(0 . . . 11) 96 for modules 17 to 19.

When data is fetched from storage, a set of partial syndrome bits SYH(0 . . . 11) and SYL(0 . . . 11) is generated from the fetched data word from the DRAM array chips or the MDRMUX as illustrated in detail by the following equation:

    __________________________________________________________________________     /******** FETCH ECC ******************************************************     **********/                                                                    /*************************************************************************     ************/                                 /*>                              CHECKBIT REGENERATION             <*/                                          /*************************************************************************     ************/                                                                  SYH(0):= OPA                                                                           (MDRMUX.sub.-- H(0)                                                                      ||MDRMUX.sub.-- H(4)                                                   ||MDRMUX.sub.-- H(8)                                                   ||MDRMUX.sub.--                                              H(12)                                    |                                                                             |MDRMUX.sub.-- H(16)                                                            ||MDRMUX.sub.-- H(20)                                                  ||MDRMUX.sub.-- H(24)                                                  ||MDRMUX.sub.--                                              H(28));                                  SYL(0):= OPA                                                                           (MDRMUX.sub.-- L(0)                                                                      ||MDRMUX.sub.-- L(3)                                                   ||MDRMUX.sub.-- L(4)                                                   ||MDRMUX.sub.--                                              L(5)                                     |                                                                             |MDRMUX.sub.-- L(7)                                                             ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.-- L(9)                                                   ||MDRMUX.sub.--                                              L(10)                                    |                                                                             |MDRMUX.sub.-- L(11)                                                            ||MDRMUX.sub.-- L(14)                                                  ||MDRMUX.sub.-- L(15)                                                  ||MDRMUX.sub.--                                              L(16)                                    |                                                                             |MDRMUX.sub.-- L(17)                                                            ||MDRMUX.sub.-- L(20)                                                  ||MDRMUX.sub.-- L(21)                                                  ||MDRMUX.sub.--                                              L(24)                                    |                                                                             |MDRMUX.sub.-- L(25)                                                            ||MDRMUX.sub.-- L(26)                                                  ||MDRMUX.sub.-- L(29)                                                  ||MDRMUX.sub.--                                              L(30));                                  SYH(1):= OPA                                                                           (MDRMUX.sub.-- H(1)                                                                      ||MDRMUX.sub.-- H(5)                                                   ||MDRMUX.sub.-- H(9)                                                   ||MDRMUX.sub.--                                              H(13)                                    |                                                                             |MDRMUX.sub.-- H(17)                                                            ||MDRMUX.sub.-- H(21)                                                  ||MDRMUX.sub.-- H(25)                                                  ||MDRMUX.sub.--                                              H(29));                                  SYL(1):= OPA                                                                           (MDRMUX.sub.-- L(1)                                                                      ||MDRMUX.sub.-- L(2)                                                   ||MDRMUX.sub.-- L(3)                                                   ||MDRMUX.sub.--                                              L(4)                                     |                                                                             |MDRMUX.sub.-- L(6)                                                             ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.--                                              L(10)                                    |                                                                             |MDRMUX.sub.-- L(14)                                                            ||MDRMUX.sub.-- L(16)                                                  ||MDRMUX.sub.-- L(20)                                                  ||MDRMUX.sub.--                                              L(24)                                    |                                                                             |MDRMUX.sub.-- L(27)                                                            ||MDRMUX.sub.-- L(28)                                                  ||MDRMUX.sub.-- L(29)                                                  ||MDRMUX.sub.--                                              L(31));                                  SYH(2):= OPA                                                                           (MDRMUX.sub.-- H(2)                                                                      ||MDRMUX.sub.-- H(6)                                                   ||MDRMUX.sub.-- H(10)                                                  ||MDRMUX.sub.--                                              H(14)                                    |                                                                             |MDRMUX.sub.-- H(18)                                                            ||MDRMUX.sub.-- H(22)                                                  ||MDRMUX.sub.-- H(26)                                                  ||MDRMUX.sub.--                                              H(30));                                  SYL(2):= OPA                                                                           (MDRMUX.sub.-- L(1)                                                                      ||MDRMUX.sub.-- L(2)                                                   ||MDRMUX.sub.-- L(3)                                                   ||MDRMUX.sub.--                                              L(5)                                     |                                                                             |MDRMUX.sub.-- L(6)                                                             ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.-- L(9)                                                   ||MDRMUX.sub.--                                              L(12)                                    |                                                                             |MDRMUX.sub.-- L(13)                                                            ||MDRMUX.sub.-- L(14)                                                  ||MDRMUX.sub.-- L(15)                                                  ||MDRMUX.sub.--                                              L(18)                                    |                                                                             |MDRMUX.sub.-- L(19)                                                            ||MDRMUX.sub.-- L(22)                                                  ||MDRMUX.sub.-- L(23)                                                  ||MDRMUX.sub.--                                              L(24)                                    |                                                                             |MDRMUX.sub.-- L(27)                                                            ||MDRMUX.sub.-- L(28)                                                  ||MDRMUX.sub.-- L(30)                                                  ||MDRMUX.sub.--                                              L(31));                                  SYH(3):= OPA                                                                           (MDRMUX.sub.-- H(3)                                                                      ||MDRMUX.sub.-- H(7)                                                   ||MDRMUX.sub.-- H(11)                                                  ||MDRMUX.sub.--                                              H(15)                                    |                                                                             |MDRMUX.sub.-- H(19)                                                            ||MDRMUX.sub.-- H(23)                                                  ||MDRMUX.sub.-- H(27)                                                  ||MDRMUX.sub.--                                              H(31));                                  SYL(3):= OPA                                                                           (MDRMUX.sub.-- L(0)                                                                      ||MDRMUX.sub.-- L(1)                                                   ||MDRMUX.sub.-- L(2)                                                   ||MDRMUX.sub.--                                              L(4)                                     |                                                                             |MDRMUX.sub.-- L(5)                                                             ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.--                                              L(12)                                    |                                                                             |MDRMUX.sub.-- L(14)                                                            ||MDRMUX.sub.-- L(18)                                                  ||MDRMUX.sub.-- L(22)                                                  ||MDRMUX.sub.--                                              L(25)                                    |                                                                             |MDRMUX.sub.-- L(26)                                                            ||MDRMUX.sub.-- L(27)                                                  ||MDRMUX.sub.-- L(29)                                                  ||MDRMUX.sub.--                                              L(30));                                  SYH(4):= OPA                                                                           (MDRMUX.sub.-- H(1)                                                                      ||MDRMUX.sub.-- H(2)                                                   ||MDRMUX.sub.-- H(4)                                                   ||MDRMUX.sub.--                                              H(10)                                    |                                                                             |MDRMUX.sub.-- H(12)                                                            ||MDRMUX.sub.-- H(14)                                                  ||MDRMUX.sub.-- H(15)                                                  ||MDRMUX.sub.--                                              H(16)                                    |                                                                             |MDRMUX.sub.-- H(18)                                                            ||MDRMUX.sub.-- H(20)                                                  ||MDRMUX.sub.-- H(21)                                                  ||MDRMUX.sub.--                                              H(23)                                    |                                                                             |MDRMUX.sub.-- H(25)                                                            ||MDRMUX.sub.-- H(27)                                                  ||MDRMUX.sub.-- H(28)                                                  ||MDRMUX.sub.--                                              H(29)                                    |                                                                             |MDRMUX.sub.-- H(30));                                        SYL(4):= OPA                                                                           (MDRMUX.sub.-- L(0)                                                                      ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.--                                              L(13)                                    |                                                                             |MDRMUX.sub.-- L(14)                                                            ||MDRMUX.sub.-- L(15)                                                  ||MDRMUX.sub.-- L(16)                                                  ||MDRMUX.sub.--                                              L(20)                                    |                                                                             |MDRMUX.sub.-- L(21)                                                            ||MDRMUX.sub.-- L(22)                                                  ||MDRMUX.sub.-- L(24)                                                  ||MDRMUX.sub.--                                              L(29));                                  SYH(5):= OPA                                                                           (MDRMUX.sub.-- H(0)                                                                      ||MDRMUX.sub.-- H(1)                                                   ||MDRMUX.sub.-- H(3)                                                   ||MDRMUX.sub.--                                              H(5)                                     |                                                                             |MDRMUX.sub.-- H(11)                                                            ||MDRMUX.sub.-- H(13)                                                  ||MDRMUX.sub.-- H(14)                                                  ||MDRMUX.sub.--                                              H(17)                                    |                                                                             |MDRMUX.sub.-- H(19)                                                            ||MDRMUX.sub.-- H(20)                                                  ||MDRMUX.sub.-- H(22)                                                  ||MDRMUX.sub.--                                              H(23)                                    |                                                                             |MDRMUX.sub.-- H(24)                                                            ||MDRMUX.sub.-- H(25)                                                  ||MDRMUX.sub.-- H(26)                                                  ||MDRMUX.sub.--                                              H(27)                                    |                                                                             |MDRMUX.sub.-- H(28)                                                            ||MDRMUX.sub.-- H(31));                    SYL(5):= OPA                                                                           (MDRMUX.sub.-- L(1)                                                                      ||MDRMUX.sub.-- L(6)                                                   ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.--                                              L(9)                                     |                                                                             |MDRMUX.sub.-- L(12)                                                            ||MDRMUX.sub.-- L(13)                                                  ||MDRMUX.sub.-- L(14)                                                  ||MDRMUX.sub.--                                              L(17)                                    |                                                                             |MDRMUX.sub.-- L(20)                                                            ||MDRMUX.sub.-- L(23)                                                  ||MDRMUX.sub.-- L(25)                                                  ||MDRMUX.sub.--                                              L(28)                                    |                                                                             |MDRMUX.sub.-- L(29));                                        SYH(6):= OPA                                                                           (MDRMUX.sub.-- H(0)                                                                      ||MDRMUX.sub.-- H(2)                                                   ||MDRMUX.sub.-- H(3)                                                   ||MDRMUX.sub.--                                              H(6)                                     |                                                                             |MDRMUX.sub.-- H(8)                                                             ||MDRMUX.sub.-- H(10)                                                  ||MDRMUX.sub.-- H(12)                                                  ||MDRMUX.sub.--                                              H(13)                                    |                                                                             |MDRMUX.sub.-- H(15)                                                            ||MDRMUX.sub.-- H(16)                                                  ||MDRMUX.sub.-- H(21)                                                  ||MDRMUX.sub.--                                              H(22)                                    |                                                                             |MDRMUX.sub.-- H(25)                                                            ||MDRMUX.sub.-- H(28)                                                  ||MDRMUX.sub.-- H(31));          SYL(6):= OPA                                                                           (MDRMUX.sub.-- L(2)                                                                      ||MDRMUX.sub.-- L(5)                                                   ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.--                                              L(10                                     |                                                                             |MDRMUX.sub.-- L(12)                                                            ||MDRMUX.sub.-- L(13)                                                  ||MDRMUX.sub.-- L(14)                                                  ||MDRMUX.sub.--                                              L(18)                                    |                                                                             |MDRMUX.sub.-- L(20)                                                            ||MDRMUX.sub.-- L(23)                                                  ||MDRMUX.sub.-- L(26)                                                  ||MDRMUX.sub.--                                              L(31));                                  SYH(7):= OPA                                                                           (MDRMUX.sub.-- H(1)                                                                      ||MDRMUX.sub.-- H(2)                                                   ||MDRMUX.sub.-- H(7)                                                   ||MDRMUX.sub.--                                              H(9)                                     |                                                                             |MDRMUX.sub.-- H(11)                                                            ||MDRMUX.sub.-- H(12)                                                  ||MDRMUX.sub.-- H(14)                                                  ||MDRMUX.sub.--                                              H(15)                                    |                                                                             |MDRMUX.sub.-- H(17)                                                            ||MDRMUX.sub.-- H(20)                                                  ||MDRMUX.sub.-- H(21)                                                  ||MDRMUX.sub.--                                              H(23)                                    |                                                                             |MDRMUX.sub.-- H(24)                                                            ||MDRMUX.sub.-- H(25)                                                  ||MDRMUX.sub.-- H(29)                                                  ||MDRMUX.sub.--                                              H(30)                                    |                                                                             |MDRMUX.sub.-- H(31));                                        SYL(7):= OPA                                                                           (MDRMUX.sub.-- L(3)                                                                      ||MDRMUX.sub.-- L(4)                                                   ||MDRMUX.sub.-- L(5)                                                   ||MDRMUX.sub.--                                              L(6)                                     |                                                                             |MDRMUX.sub.-- L(7)                                                             ||MDRMUX.sub.-- L(11)                                                  ||MDRMUX.sub.-- L(12)                                                  ||MDRMUX.sub.--                                              L(15)                                    |                                                                             |MDRMUX.sub.-- L(19)                                                            ||MDRMUX.sub.-- L(21)                                                  ||MDRMUX.sub.-- L(22)                                                  ||MDRMUX.sub.--                                              L(23)                                    |                                                                             |MDRMUX.sub.-- L(27)                                                            ||MDRMUX.sub.-- L(30)                                                  ||MDRMUX.sub.-- L(31));          SYH(8):= OPA                                                                           (MDRMUX.sub.-- H(0)                                                                      ||MDRMUX.sub.-- H(4)                                                   ||MDRMUX.sub.-- H(5)                                                   ||MDRMUX.sub.--                                              H(6)                                     |                                                                             |MDRMUX.sub.-- H(9)                                                             ||MDRMUX.sub.-- H(10)                                                  ||MDRMUX.sub.-- H(11)                                                  ||MDRMUX.sub.--                                              H(12)                                    |                                                                             |MDRMUX.sub.-- H(14)                                                            ||MDRMUX.sub.-- H(16)                                                  ||MDRMUX.sub.-- H(19)                                                  ||MDRMUX.sub.--                                              H(22)                                    |                                                                             |MDRMUX.sub.-- H(25)                                                            ||MDRMUX.sub.-- H(26)                                                  ||MDRMUX.sub.-- H(31));          SYL(8):= OPA                                                                           (MDRMUX.sub.-- L(1)                                                                      ||MDRMUX.sub.-- L(3)                                                   ||MDRMUX.sub.-- L(4)                                                   ||MDRMUX.sub.--                                              L(8)                                     |                                                                             |MDRMUX.sub.-- L(10)                                                            ||MDRMUX.sub.-- L(11)                                                  ||MDRMUX.sub.-- L(12)                                                  ||MDRMUX.sub.--                                              L(17)                                    |                                                                             |MDRMUX.sub.-- L(18)                                                            ||MDRMUX.sub.-- L(20)                                                  ||MDRMUX.sub.-- L(25)                                                  ||MDRMUX.sub.--                                              L(28));                                  SYH(9):= OPA                                                                           (MDRMUX.sub.-- H(1)                                                                      ||MDRMUX.sub.-- H(4)                                                   ||MDRMUX.sub.-- H(7)                                                   ||MDRMUX.sub.--                                              H(8)                                     |                                                                             |MDRMUX.sub.-- H(9)                                                             ||MDRMUX.sub.-- H(10)                                                  ||MDRMUX.sub.-- H(13)                                                  ||MDRMUX.sub.--                                              H(15)                                    |                                                                             |MDRMUX.sub.-- H(17)                                                            ||MDRMUX.sub.-- H(18)                                                  ||MDRMUX.sub.-- H(19)                                                  ||MDRMUX.sub.--                                              H(23)                                    |                                                                             |MDRMUX.sub.-- H(24)                                                            ||MDRMUX.sub.-- H(25)                                                  ||MDRMUX.sub.-- H(27)                                                  ||MDRMUX.sub.--                                              H(30)                                    |                                                                             |MDRMUX.sub.-- H(31));                                        SYL(9):= OPA                                                                           (MDRMUX.sub.-- L(0)                                                                      ||MDRMUX.sub.-- L(1)                                                   ||MDRMUX.sub.-- L(2)                                                   ||MDRMUX.sub.--                                              L(3)                                     |                                                                             |MDRMUX.sub.-- L(5)                                                             ||MDRMUX.sub.-- L(9)                                                   ||MDRMUX.sub.-- L(10)                                                  ||MDRMUX.sub.--                                              L(13)                                    |                                                                             |MDRMUX.sub.-- L(16)                                                            ||MDRMUX.sub.-- L(17)                                                  ||MDRMUX.sub.-- L(19)                                                  ||MDRMUX.sub.--                                              L(21)                                    |                                                                             |MDRMUX.sub.-- L(24)                                                            ||MDRMUX.sub.-- L(25)                                                  ||MDRMUX.sub.-- L(29));          SYH(10):=OPA                                                                           (MDRMUX.sub.-- H(2)                                                                      ||MDRMUX.sub.-- H(4)                                                   ||MDRMUX.sub.-- H(7)                                                   ||MDRMUX.sub.--                                              H(8)                                     |                                                                             |MDRMUX.sub.-- H(9)                                                             ||MDRMUX.sub.-- H(10)                                                  ||MDRMUX.sub.-- H(12)                                                  ||MDRMUX.sub.--                                              H(17)                                    |                                                                             |MDRMUX.sub.-- H(18)                                                            ||MDRMUX.sub.-- H(19)                                                  ||MDRMUX.sub.-- H(20)                                                  ||MDRMUX.sub.--                                              H(22)                                    |                                                                             |MDRMUX.sub.-- H(24)                                                            ||MDRMUX.sub.-- H(26)                                                  ||MDRMUX.sub.-- H(27)                                                  ||MDRMUX.sub.--                                              H(29)                                    |                                                                             |MDRMUX.sub.-- H(31));                                        SYL(10):=OPA                                                                           (MDRMUX.sub.-- L(1)                                                                      ||MDRMUX.sub.-- L(6)                                                   ||MDRMUX.sub.-- L(8)                                                   ||MDRMUX.sub.--                                              L(9)                                     |                                                                             |MDRMUX.sub.-- L(11)                                                            ||MDRMUX.sub.-- L(14)                                                  ||MDRMUX.sub.-- L(16)                                                  ||MDRMUX.sub.--                                              L(18)                                    |                                                                             |MDRMUX.sub.-- L(19)                                                            ||MDRMUX.sub.-- L(22)                                                  ||MDRMUX.sub.-- L(27)                                                  ||MDRMUX.sub.--                                              L(30));                                  SYH(11):=OPA                                                                           (MDRMUX.sub.-- H(3)                                                                      ||MDRMUX.sub.-- H(5)                                                   ||MDRMUX.sub.-- H(6)                                                   ||MDRMUX.sub.--                                              H(7)                                     |                                                                             |MDRMUX.sub.-- H(8)                                                             ||MDRMUX.sub.-- H(11)                                                  ||MDRMUX.sub.-- H(13)                                                  ||MDRMUX.sub.--                                              H(16)                                    |                                                                             |MDRMUX.sub.-- H(17)                                                            ||MDRMUX.sub.-- H(18)                                                  ||MDRMUX.sub.-- H(21)                                                  ||MDRMUX.sub.--                                              H(23)                                    |                                                                             |MDRMUX.sub.-- H(25)                                                            ||MDRMUX.sub.-- H(26)                                                  ||MDRMUX.sub.-- H(28)                                                  ||MDRMUX.sub.--                                              H(29)                                    |                                                                             |MDRMUX.sub.-- H(30)                                                            ||MDRMUX.sub.-- H(31));                    SYL(11):=OPA                                                                           (MDRMUX.sub.-- L(0)                                                                      ||MDRMUX.sub.-- L(1)                                                   ||MDRMUX.sub.-- L(7)                                                   ||MDRMUX.sub.--                                              L(8)                                     |                                                                             |MDRMUX.sub.-- L(10)                                                            ||MDRMUX.sub.-- L(11)                                                  ||MDRMUX.sub.-- L(15)                                                  ||MDRMUX.sub.--                                              L(17)                                    |                                                                             |MDRMUX.sub.-- L(18)                                                            ||MDRMUX.sub.-- L(23)                                                  ||MDRMUX.sub.-- L(26)                                                  ||MDRMUX.sub.--                                              L(27)                                    |                                                                             |MDRMUX.sub.-- L(31));                                        __________________________________________________________________________

The same circuits that are used in generating the partial check bits during the store operations are utilized again to regenerate the partial syndrome bits. So for example, partial syndrome bit i is the Exclusive-OR of the fetched data word at positions specified by 1's in the ith row of the parity check matrix. That is to say that the partial syndrome bits are generated by supplying specified signals to a set of exclusive₋₋ OR gates.

The syndrome bits SY(0 . . . 11) are then generated from the combination of the fetched data from check bits MDRMUX₋₋ C(0 . . . 11) and the address parity bits from Fetch₋₋ ADDRP(0. . . m) which are regenerated from the incoming system address bits.

    __________________________________________________________________________     /******************************* Syndrome Generation *********************     **********/                                                                    SY(0)   :=                                                                     MDRMUX.sub.-- C(0)                                                                      XOR SYH(0)                                                                            XOR SYL(0)  XOR FETCH.sub.-- ADDRP(1);                         SY(1)   :=                                                                     MDRMUX.sub.-- C(1)                                                                      XOR SYH(1)                                                                            XOR SYL(1)                                                                     XOR FETCH.sub.-- ADDRP(0)                                                                  XOR FETCH_ADDRP(1);                                SY(2)   :=                              ;                                      MDRMUX.sub.-- C(2)                                                                      XOR SYH(2)                                                                            XOR SYL(2) XOR FETCH_ADDRP(0)                                  SY(3)   :=                                                                     MDRMUX.sub.-- C(3)                                                                      XOR SYH(3)                                                                            XOR SYL(3)                                                                     XOR FETCH ADDRP(0)                                                                         XOR FETCH_ADDRP(1);                                SY(4)   :=                              ;                                      MDRMUX.sub.-- C(4)                                                                      XOR SYH(4)                                                                            XOR SYL(4) XOR FETCH_ADDRP(0)                                  SY(5)   :=                                                                     MDRMUX.sub.-- C(5)                                                                      XOR SYH(5)                                                                            XOR SYL(5)  XOR FETCH ADDRP(1);                                SY(6)   :=                                                                     MDRMUX.sub.-- C(6)                                                                      XOR SYH(6)                                                                            XOR SYL(6)              ;                                      SY(7)   :=                                                                     MDRMUX.sub.-- C(7)                                                                      XOR SYH(7)                                                                            XOR SYL(7)              ;                                      SY(8)   :=                                                                     MDRMUX.sub.-- C(8)                                                                      XOR SYH(8)                                                                            XOR SYL(8)              ;                                      SY(9)   :=                                                                     MDRMUX.sub.-- C(9)                                                                      XOR SYH(9)                                                                            XOR SYL(9)              ;                                      SY(10)   :=                                                                    MDRMUX.sub.-- C(10)                                                                     XOR SYH(10)                                                                           XOR SYL(10) XOR FETCH_ADDRP(1);                                SY(11)   :=                                                                    MDRMUX.sub.-- C(11)                                                                     XOR SYH(11)                                                                           XOR SYL(11) XOR FETCH_ADDRP(0)                                                                         ;                                      __________________________________________________________________________

The partial syndrome bits SY(0 . . . 11) 72 are then decoded 74 to identify any possible errors as illustrated in FIG. 7. Module error indicators are then generated according to the formula given below during the decoding process to detect and indicate errors.

    __________________________________________________________________________      ##STR13##                                                                     MOD.sub.-- 00 :=                                                                      (    SY( 1) XOR SY( 2)    XOR  SY( 4) )                                 &      ( SY( 0)                                                                            XOR SY( 1)    XOR SY( 3)                                                                            XOR  SY( 5) )                                 &      ( SY( 0)    XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 6) )                                 &      (    SY( 1) XOR SY( 2)    XOR  SY( 7) )                                 &      ( SY( 0)                  XOR  SY( 8) )                                 &      (    SY( 1)               XOR  SY( 9) )                                 &      (           SY( 2)        XOR  SY(10) )                                 &      (                  SY( 3) XOR  SY(11) );                                MOD.sub.-- 01 :=                                                                      ( SY( 0)                  XOR  SY( 4) )                                 &      (    SY( 1)               XOR  SY( 5) )                                 &      (           SY( 2)        XOR  SY( 6) )                                 &      (                  SY( 3) XOR  SY( 7) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)    XOR  SY( 8) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY( 9) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY(10) )                                 &      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY(11) );                                MOD.sub.-- 02 :=                                                                      (           SY( 2)        XOR  SY( 4) )                                 &      (                  SY( 3) XOR  SY( 5) )                                 &      ( SY( 0)    XOR SY( 2)    XOR  SY( 6) )                                 &      (    SY( 1)        XOR SY( 3)                                                                            XOR  SY( 7) )                                 &      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 8) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)    XOR  SY( 9) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)    XOR  SY(10) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY(11) );                                MOD.sub.-- 03 :=                                                                      ( SY( 0)    XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 4) )                                 &      (    SY( 1) XOR SY( 2)    XOR  SY( 5) )                                 &      ( SY( 0)                                                                            XOR SY( 1)    XOR SY( 3)                                                                            XOR  SY( 6) )                                 &      ( SY( 0)    XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 7) )                                 &      ( SY( 0)    XOR SY( 2)    XOR  SY( 8) )                                 &      (    SY( 1)        XOR SY( 3)                                                                            XOR  SY( 9) )                                 &      ( SY( 0)                  XOR  SY(10) )                                 &      (    SY( 1)               XOR  SY(11) );                                MOD.sub.-- 04 :=                                                                      ( SY( 0)    XOR SY( 2)    XOR  SY( 4) )                                 &      (    SY( 1)        XOR SY( 3)                                                                            XOR  SY( 5) )                                 &      ( SY( 0)                  XOR  SY( 6) )                                 &      (    SY( 1)               XOR  SY( 7) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY( 8) )                                 &      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 9) )                                 &      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY(10) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)    XOR  SY(11) );                                MOD.sub.-- 05 :=                                                                      ( SY( 0)                                                                            XOR SY( 1)    XOR SY( 3)                                                                            XOR  SY( 4) )                                 &      ( SY( 0)    XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 5) )                                 &      (    SY( 1) XOR SY( 2)    XOR  SY( 6) )                                 &      ( SY( 0)                                                                            XOR SY( 1)    XOR SY( 3)                                                                            XOR  SY( 7) )                                 &      (           SY( 2)        XOR  SY( 8) )                                 &      (                  SY( 3) XOR  SY( 9) )                                 &      ( SY( 0)    XOR SY( 2)    XOR  SY(10) )                                 &      (    SY( 1)        XOR SY( 3)                                                                            XOR  SY(11) );                                MOD.sub.-- 06 :=                                                                      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 4) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 5) )                                 &      (    SY( 1)               XOR  SY( 6) )                                 &      ( SY( 0)                                                                            XOR SY( 1)           XOR  SY( 7) )                                 &      (    SY( 1) XOR SY( 2)    XOR  SY( 8) )                                 &      ( SY( 0)                                                                            XOR SY( 1)    XOR SY( 3)                                                                            XOR  SY( 9) )                                 &      ( SY( 0)    XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY(10) )                                 &      (    SY( 1) XOR SY( 2)    XOR  SY(11) );                                MOD.sub.-- 07 :=                                                                      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)    XOR  SY( 4) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY( 5) )                                 &      ( SY( 0)           XOR SY( 3)                                                                            XOR  SY( 6) )                                 &      (    SY( 1) XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY( 7) )                                 &      (                  SY( 3) XOR  SY( 8) )                                 &      (           SY( 2) XOR SY( 3)                                                                            XOR  SY( 9) )                                 &      (    SY( 1)        XOR SY( 3)                                                                            XOR  SY(10) )                                 &      ( SY( 0)                                                                            XOR SY( 1)                                                                            XOR SY( 2)                                                                            XOR SY( 3)                                                                            XOR  SY(11) );                                MOD.sub.-- 08 :=                                                                      ( SY( 4)           XOR SY( 7)                                                                            XOR  SY( 0) )                                 &      (    SY( 5) XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 1) )                                 &      (    SY( 5) XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 2) )                                 &      ( SY( 4)                                                                            XOR SY( 5)                                                                            XOR SY( 6)    XOR  SY( 3) )                                 &      (    SY( 5)        XOR SY( 7)                                                                            XOR  SY( 8) )                                 &      ( SY( 4)                                                                            XOR SY( 5)                                                                            XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 9) )                                 &      (    SY( 5)               XOR  SY(10) )                                 &      ( SY( 4)                                                                            XOR SY( 5)           XOR  SY(11) );                                MOD.sub.-- 09 :=                                                                      ( SY( 8)                                                                            XOR SY( 9)    XOR SY(11)                                                                            XOR  SY( 0) )                                 &      ( SY( 8)    XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 1) )                                 &      (    SY( 9) XOR SY(10)    XOR  SY( 2) )                                 &      ( SY( 8)                                                                            XOR SY( 9)    XOR SY(11)                                                                            XOR  SY( 3) )                                 &      (                  SY(11) XOR  SY( 4) )                                 &      (           SY(10) XOR SY(11)                                                                            XOR  SY( 5) )                                 &      (    SY( 9)        XOR SY(11)                                                                            XOR  SY( 6) )                                 &      ( SY( 8)                                                                            XOR SY( 9)                                                                            XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 7) );                                MOD.sub.-- 10 :=                                                                      ( SY( 4)                                                                            XOR SY( 5)                                                                            XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 0) )                                 &      ( SY( 4)    XOR SY( 6)    XOR  SY( 1) )                                 &      ( SY( 4)                                                                            XOR SY( 5)           XOR  SY( 2) )                                 &      ( SY( 4)                  XOR  SY( 3) )                                 &      ( SY( 4)    XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 8) )                                 &      (    SY( 5) XOR SY( 6)    XOR  SY( 9) )                                 &      ( SY( 4)                                                                            XOR SY( 5)    XOR SY( 7)                                                                            XOR  SY(10) )                                 &      ( SY( 4)    XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY(11) );                                MOD.sub.-- 11 :=                                                                      (           SY(10) XOR SY(11)                                                                            XOR  SY( 0) )                                 &      (           SY(10)        XOR  SY( 1) )                                 &      ( SY( 8)                                                                            XOR SY( 9)                                                                            XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 2) )                                 &      ( SY( 8)    XOR SY(10)    XOR  SY( 3) )                                 &      (    SY( 9) XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 4) )                                 &      ( SY( 8)                                                                            XOR SY( 9)                                                                            XOR SY(10)    XOR  SY( 5) )                                 &      ( SY( 8)                                                                            XOR SY( 9)                                                                            XOR SY(10)    XOR  SY( 6) )                                 &      ( SY( 8)                  XOR  SY( 7) );                                MOD.sub.-- 12 :=                                                                      ( SY( 4)                                                                            XOR SY( 5)           XOR  SY( 0) )                                 &      ( SY( 4)                  XOR  SY( 1) )                                 &      (           SY( 6) XOR SY( 7)                                                                            XOR  SY( 2) )                                 &      (           SY( 6)        XOR  SY( 3) )                                 &      (    SY( 5) XOR SY( 6)    XOR  SY( 8) )                                 &      ( SY( 4)                                                                            XOR SY( 5)    XOR SY( 7)                                                                            XOR  SY( 9) )                                 &      ( SY( 4)    XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY(10) )                                 &      (    SY( 5) XOR SY( 6)    XOR  SY(11) );                                MOD.sub.-- 13 :=                                                                      ( SY( 8)                                                                            XOR SY( 9)           XOR  SY( 0) )                                 &      ( SY( 8)                  XOR  SY( 1) )                                 &      (           SY(10) XOR SY(11)                                                                            XOR  SY( 2) )                                 &      (           SY(10)        XOR  SY( 3) )                                 &      ( SY( 8)                                                                            XOR SY( 9)                                                                            XOR SY(10)    XOR  SY( 4) )                                 &      ( SY( 8)           XOR SY(11)                                                                            XOR  SY( 5) )                                 &      ( SY( 8)           XOR SY(11)                                                                            XOR  SY( 6) )                                 &      (    SY( 9) XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 7) );                                MOD.sub.-- 14 :=                                                                      ( SY( 4)                                                                            XOR SY( 5)                                                                            XOR SY( 6)    XOR  SY( 0) )                                 &      ( SY( 4)           XOR SY( 7)                                                                            XOR  SY( 1) )                                 &      ( SY( 4)           XOR SY( 7)                                                                            XOR  SY( 2) )                                 &      (    SY( 5) XOR SY( 6)                                                                            XOR SY( 7)                                                                            XOR  SY( 3) )                                 &      (    SY( 5)               XOR  SY( 8) )                                 &      ( SY( 4)                                                                            XOR SY( 5)           XOR  SY( 9) )                                 &      (                  SY( 7) XOR  SY(10) )                                 &      (           SY( 6) XOR SY( 7)                                                                            XOR  SY(11) );                                MOD.sub.-- 15 :=                                                                      (    SY( 9) XOR SY(10)    XOR  SY( 0) )                                 &      ( SY( 8)                                                                            XOR SY( 9)    XOR SY(11)                                                                            XOR  SY( 1) )                                 &      ( SY( 8)    XOR SY(10)                                                                            XOR SY(11)                                                                            XOR  SY( 2) )                                 &      (    SY( 9) XOR SY(10)    XOR  SY( 3) )                                 &      (    SY( 9)               XOR  SY( 4) )                                 &      ( SY( 8)                                                                            XOR SY( 9)           XOR  SY( 5) )                                 &      (                  SY(11) XOR  SY( 6) )                                 &      (           SY(10) XOR SY(11)                                                                            XOR  SY( 7) );                                MOD.sub.-- 16 :=                                                                      (                          SY( 4) )                                     &      (                          SY( 5) )                                     &      (                          SY( 6) )                                     &      (                          SY( 7) )                                     &      (                          SY( 8) )                                     &      (                          SY( 9) )                                     &      (                          SY(10) )                                     &      (                          SY(11) );                                    MOD.sub.-- 17 :=                                                                      (                          SY( 0) )                                     &      (                          SY( 1) )                                     &      (                          SY( 2) )                                     &      (                          SY( 3) )                                     &      (                          SY( 8) )                                     &      (                          SY( 9) )                                     &      (                          SY(10) )                                     &      (                          SY(11) );                                    MOD.sub.-- 18 :=                                                                      (                          SY( 0) )                                     &      (                          SY( 1) )                                     &      (                          SY( 2) )                                     &      (                          SY( 3) )                                     &      (                          SY( 4) )                                     &      (                          SY( 5) )                                     &      (                          SY( 6) )                                     &      (                          SY( 7) );                                    __________________________________________________________________________

FIG. 8 illustrates a set of module errors indicators MOD₋₋ 00, MOD₋₋ 01, . . . MOD₋₋ 18 74. Any error will cause the setting of one of the MOD's. For example an error in module 0 will cause MOD₋₋ 00 to be set to 1. During the decoding operations, bit error indicators are also generated from circuit lines which are later used to invert the fetched data bits to correct certain errors. Invert lines 81 INV₋₋ H(0 . . . 31) 84, INV₋₋ L(0 . . . 31), and INV₋₋ C(0 . . . 11) are used in conjunction with bit errors so that when a bit error indicator is on, the corresponding data bit is corrected by inversion of the data. Bit error indicators 82 are generated from the following equations.

    ______________________________________                                         /********************** Invert Enabling ***********************/               ______________________________________                                         INV.sub.-- H(0..3)                                                                          :=      MOD.sub.-- 00                                                                            GATE SY(0..3);                                  INV.sub.-- H(4..7)                                                                          :=      MOD.sub.-- 01                                                                            GATE SY(0..3);                                  INV.sub.-- H(8..11)                                                                         :=      MOD.sub.-- 02                                                                            GATE SY(0..3);                                  INV.sub.-- H(12..15)                                                                        :=      MOD.sub.-- 03                                                                            GATE SY(0..3);                                  INV.sub.-- H(16..19)                                                                        :=      MOD.sub.-- 04                                                                            GATE SY(0..3);                                  INV.sub.-- H(20..23)                                                                        :=      MOD.sub.-- 05                                                                            GATE SY(0..3);                                  INV.sub.-- H(24..27)                                                                        :=      MOD.sub.-- 06                                                                            GATE SY(0..3);                                  INV.sub.-- H(28..31)                                                                        :=      MOD.sub.-- 07                                                                            GATE SY(0..3);                                  INV.sub.-- L(0..3)                                                                          :=      MOD.sub.-- 08                                                                            GATE SY(4..7);                                  INV.sub.-- L(4..7)                                                                          :=      MOD.sub.-- 09                                                                            GATE SY(8..11);                                 INV.sub.-- L(8..11)                                                                         :=      MOD.sub.-- 10                                                                            GATE SY(4..7);                                  INV.sub.-- L(12..15)                                                                        :=      MOD.sub.-- 11                                                                            GATE SY(8..11);                                 INV.sub.-- L(16..19)                                                                        :=      MOD.sub.-- 12                                                                            GATE SY(4..7);                                  INV.sub.-- L(20..23)                                                                        :=      MOD.sub.-- 13                                                                            GATE SY(8..11);                                 INV.sub.-- L(24..27)                                                                        :=      MOD.sub.-- 14                                                                            GATE SY(4..7);                                  INV.sub.-- L(28..31)                                                                        :=      MOD.sub.-- 15                                                                            GATE SY(8..11);                                 INV.sub.-- C(0..3)                                                                          :=      MOD.sub.-- 16                                                                            GATE SY(0..3);                                  INV.sub.-- C(4..7)                                                                          :=      MOD.sub.-- 17                                                                            GATE SY(4..7);                                  INV.sub.-- C(8..11)                                                                         :=      MOD.sub.-- 18                                                                            GATE SY(8..11);                                 ______________________________________                                    

In this manner, the status of the module error and the syndromes are to enable a plurality of invert lines and generate other signals pertaining to types of errors 78 including a UE (Uncorrectable error) signal 79 or a CE (Correctable Error) signal 77.

    __________________________________________________________________________     /**************************** Error Indication ***************************     **/                                                                            ECC.sub.-- ANYE :=                                                                     SY(0)                                                                              |                                                                       SY(1)                                                                              |                                                                       SY(2)                                                                              |                                                                       SY(3)                                                        SY(4)                                                                              |                                                                       SY(5)                                                                              |                                                                       SY(6)                                                                              |                                                                       SY(7)                                                        SY(8)                                                                              |                                                                       SY(9)                                                                              |                                                                       SY(10)                                                                             |                                                                       SY(11)                                                                             ;                                                ECC.sub.-- CE                                                                          := (                                                                              MOD.sub.-- 00 |                                                             MOD.sub.-- 01 |                                                             MOD.sub.-- 02 |                                                             MOD.sub.-- 03 |                                     MOD.sub.-- 04 |                                                             MOD.sub.-- 05 |                                                             MOD.sub.-- 06 |                                                             MOD.sub.-- 07 |                                     MOD.sub.-- 08 |                                                             MOD.sub.-- 09 |                                                             MOD.sub.-- 10 |                                                             MOD.sub.-- 11 |                                     MOD.sub.-- 12 |                                                             MOD.sub.-- 13 |                                                             MOD.sub.-- 14 |                                                             MOD.sub.-- 15 |                                     MOD.sub.-- 16 |                                                             MOD.sub.-- 17 |                                                             MOD.sub.-- 18 |                                                                 );                                            ECC.sub.-- UCE                                                                         := ECC.sub.-- ANYE &  ECC.sub.-- CE;                                   /********************************************************************/         /*>                                                                            INVERT  AND FETCH.sub.-- ECC.sub.-- OUTPUT     <*/                             /***********************************************************************/      STEP3.sub.-- IN.sub.-- H(0..31) := MDRMUX.sub.-- OUT.sub.-- H(0..31) XOR       INV.sub.-- H(0..31);                                                           STEP3.sub.-- IN.sub.-- L(0..31) := MDRMUX.sub.-- OUT.sub.-- L(0..31) XOR       INV.sub.-- L(0..31);                                                           STEP3.sub.-- IN.sub.-- C(0..11) := MDRMUX.sub.-- OUT.sub.-- C(0..11) XOR       INV.sub.-- C(0..11);                                                           __________________________________________________________________________

FIG. 9 illustrates the arrangement of data in the memory modules on the SIMMs. There are 19 memory modules in a SIMM; a number of SIMMs can therefore be configured in this way into the memory. As illustrated, the data bits and check bits are divided into 4 bit symbols to store in 19 memory modules. SEC₋₋ O₋₋ H(0 . . . 31) are stored in modules 1 to 8, SEC₋₋ O₋₋ L(0 . . . 31) are stored in modules 9 to 16, and SEC₋₋ O₋₋ C(0 . . . 11) are stored in modules 17 to 19. The mapping of system address bits to memory modules depends on the module size as shown in Table IV and FIG. 9.

While the invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and changes therein may be effected by those skilled in the art. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention. 

We claim:
 1. A method of detecting and correcting data errors using memory modules of a computer system, said computer system having a plurality of memory modules and also having symbols which are b bits in length, said method comprising the steps of:generating a multiplicity, k, of multisegment syndrome vectors in which each segment in each of said k syndrome vector is b bits long; retrieving data stored in memory pertaining to assignment of different data blocks to a plurality of modules; generating a multiplicity of module error indicators from said syndrome vector; associating each module error indicator to at least one of said plurality of modules; setting each module error indicator to one when an error is detected in said associated module; determining where an error has occurred by analyzing all bits having a value of one in said associated error modules; and correcting all errors based on said error module values.
 2. A method of detecting and correcting data errors using memory modules in a computer system environment using a (76,64) bit code for a four-bit per chip computer memory system, said computer system having a plurality of memory modules and also having symbols which are b bits in length, said method comprising the steps of:generating a multiplicity, k, of multisegment syndrome vectors in which each segment in each of said k syndrome vector is b bits long; retrieving data stored in memory pertaining to assignment of different data blocks to a plurality of modules; generating a multiplicity of module error indicators, each from said syndrome vector, each module error indicator at least one module error bit indicator; associating each module error bit indicator with one of said plurality of modules; setting each module error bit indicator to one when an error occurs in said associated module; and determining where an error has occurred by analyzing all bits having a value of one in said associated error modules; and correcting all errors based on said error module values.
 3. The method of claim 2, wherein said error is corrected by inversion of data using said enabled invert lines.
 4. The method of claim 2, a special bit is set when multiple errors are detected in data.
 5. The method of claim 2, further including the step of determining if said error is an uncorrectable error; reporting said error as an uncorrectable error; and abandoning further efforts in correcting said error.
 6. The method of claim 2, further including the step of determining if said error is a correctable error and reporting said error as a correctable error.
 7. The method of claim 2, wherein said error is corrected by enabling a plurality of invert lines each associated with each of said modules, using information obtained from said error bit indicators and said syndrome vectors.
 8. The method of claim 2, further including the step of determining if said error is an uncorrectable error; reporting said error as an uncorrectable error; and abandoning further efforts in correcting said error.
 9. The method of claim 2, further including the step of determining if said error is a correctable error and reporting said error as a correctable error.
 10. The method of claim 2, wherein said computer system environment uses a 64 bit data bus.
 11. An apparatus for detecting and correcting data errors using memory modules in a computer system environment using a (76,64) bit code for a four-bit per chip computer memory system, said computer system having a plurality of memory modules and also having symbols which are b bits in length, said apparatus comprising:a vector generator for generating a multiplicity, k, of multisegment syndrome vectors in which each segment in each of said k syndrome vector is b bits long; a plurality of storage arrays for keeping previously stored data in said computer system's memory, said data providing assignment of different data blocks to each of said plurality of modules; a plurality of module error indicators for indicating errors in said modules by using data from said syndrome vector, said module error indicators being each associated to at least one of said plurality of modules; a bit setter for setting each module error indicator to one when an error is detected in said associated module; a determinator for determining where an error has occurred by analyzing all bits having a value of one in said associated error modules; and a corrector for correcting all errors determined based on said error module values. 